Postharvest Materials that Maintain Quality and Prevent Disorders
Diphenylamine (DPA) is an antioxidant that prevents superficial scald and can increase fruit tolerance to high carbon dioxide concentration that normally occurs in controlled atmosphere storage. Most varieties of apple treated with SmartFresh® do not require DPA for superficial scald prevention, but will have greater sensitivity to carbon dioxide in controlled atmosphere storage. After harvest, fruit can be drenched or fogged with DPA. Traditionally, fruit were drenched using the same solution more than once. This recycling drench also spread fungal spores that cause fruit decay, so a fungicide was added to the solution for grey mold and blue mold. As an alternative to the recycling drench, varieties such as Cortland may be drenched in the orchard with a nonrecycling drench. Do not add chloride to a nonrecycling drench since it will burn the fruit skin. The small volume of DPA solution used in a nonrecycling drench will reduce the efficacy of fungicides, but the need for a fungicide in nonrecycling drenches has not been clearly demonstrated. Another method of application involves fogging or by aerosol. Thermofogging DPA and fungicides circumvents the problem of solution disposal and is as effective as a recycling drench for preventing superficial scald.
1-Methylcyclopropene (1-MCP) is a relatively new postharvest chemical that interferes with ethylene, the naturally occurring plant hormone that stimulates ripening in many fruits. 1-methlycyclopropene allows storage operators to more tightly control the progression of ripening so that fruit quality can be maintained for a longer duration. When combined with cold storage or controlled atmosphere storage, it can prevent quality loss and disorders for a longer duration than cold storage alone. The commercial formulation, SmartFresh®, is currently widely used on stored apples.
Smartfresh® can maintain the crispness of apples, but works better when fruit are harvested before they are fully ripe. Because McIntosh produces high quantities of ethylene soon after harvest, it should be treated as soon as possible and preferably within three days of harvest. SmartFresh® is effective in preventing superficial scald in most varieties. Therefore, DPA is not needed, except for the variety Cortland.